What would happen if while I was popping popcorn all the kernels popped at once? Should I be concerned?
– Skye M., Portland, Maine
Don’t worry, all of your popcorn kernels won’t pop at once.
Popcorn kernels burst because the water inside them heats up and boils. When water boils it usually expands, but the hard outer hull of the core holds back the steam. For a while the steam gets hotter and hotter until the pressure rises so much that the outer hull breaks open and the pressure drops with a popping noise.
A typical bag of microwave popcorn can hold 300 grains. If all 300 burst at once, the bag could burst and create a mess, but your microwave would probably be fine. According to the 3M Noise Navigator sound insulation database, the average popcorn popper generates around 80 decibels of sound power. A sound wave that’s 300 times stronger than the sound of a typical popcorn poppers is about as loud as a nightclub and quieter than many power tools. If your microwave can survive the vibrations from around a nightclub’s speakers, it would likely survive a mega-pop.
But how likely is a mega-pop?
A popcorn kernel bursts when its internal temperature reaches around 180 degrees Celsius. The critical temperature is different for each kernel: it depends on how much moisture it contains, how strong the hull is, and how quickly your microwave is heating the particular area where the kernel is located. Most kernels take roughly the same amount of time to burst, but some happen to cross the line sooner or later than others. If we assume that they are heated independently of each other, there is no reason why they could not reach their critical internal pressure at the same time – this is just statistically unlikely.
To gauge how unlikely a mega-pop is, we need to know a little more about the timing of popcorn. I don’t usually do experiments to answer questions, but I like popcorn so I decided to collect some data in person. I put a bag of popcorn in the microwave, recorded the sound on my phone, and looked at the sound in a spectrum analyzer, which clearly showed each pop.
Evaluation of the results showed that most of the popping occurred within 30 seconds around the minute and a half.
Since a single pop lasts around 40 milliseconds, they must all burst within a 40 millisecond window to be considered “concurrent”. Using the distribution of the pops from my microwave, each kernel would have a 1 in 1,750 chance of bursting at the same time as each other. The probability that all 300 kernels burst at the same time is approximately 1 in 10⁹³⁵.
How unlikely is that?
At the time of his death in 1995, popcorn magnate Orville Redenbacher had 24 living descendants – let’s say he now has around 50 and all of them have phones with US numbers. Now you decide to speak to them. You pull out your phone and randomly pick digits. On your first round of calls, you somehow reach all 50 – without a single wrong number. When they pick up, guess their birthdays and the last four digits of their social security numbers correctly. Once you finish those calls, take out a piece of paper and write down the Mega Millions jackpot winning numbers for the next seven lottery raffles. Finally, you guess the outcome of 100 coin tosses in a row.